1. Field of the Invention
The present invention relates generally to broadband tuners. More specifically, it relates to systems and methods for image rejection from desired Radio Frequency (RF) signals.
2. Description of the Related Art
Broadband tuners are used in various electronic devices, such as televisions (TV), for transmission and reception of RF signals at particular frequencies. Broadband tuners include RF mixers that are used to convert RF signals at a particular frequency to RF signals at another frequency. This conversion is usually referred to as mixing RF signals. Mixing RF signals involves mixing of Local Oscillator (LO) signals with the input broadband signals. The output RF signals of the RF mixer usually include the desired RF and image signals. The image signals are unwanted signals that need to be rejected from the output RF signals, to provide the desired signals at the output. Filters such as SAW filters, variable bandpass filters, and polyphase filters are used to reject the image signals from the output RF signals.
Broadband tuners usually provide up to 40 dB of image rejection. Broadband TV tuners require up to 70 dB of image rejection for better transmission of the desired RF signals. In the present state of the technology, there are methods that provide up to 70 dB of image rejection. These methods require the implementation of double-conversion tuners with fixed IF SAW filters, single-conversion tuners with complex input tracking filters or single-conversion tuners with wide band matching techniques before the mixing operation. One such single conversion tuner with a double quadrature mixer is described in a publication titled “CMOS Mixers and Polyphase Filters for Large Image Rejection”, by Farbod Behbahani, Yoji Kishigami, John Leete and Asad A. Abidi, and published in IEEE Journal of Solid-State Circuits, June 2001, vol. 36, No. 6.
However, in the above methods and systems, the size of the circuit and/or its non-linearity is increased. Moreover, the wide band matching technique reduces the signal-to-noise ratio of the broadband tuners.
In light of the above, there is a need for a system and method for broadband tuning with the desired amount of image rejection. Further, the system should provide high linearity and high signal-to-noise ratio without substantially increasing the size of the circuit.